Overview

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This example shows how to create a Stateless session EJB using annotations. As stated in the "JSR 220: Enterprise JavaBeansTM,Version 3.0 - EJB Core Contracts and Requirements",

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"Stateless session beans are session beans whose instances have no conversational state. This means that all bean instances are equivalent when they are not involved in servicing a client-invoked method. The term 'stateless' signifies that an instance has no state for a specific client."

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What this means is quite simply that stateless beans are shared. They do in fact have state as you can assign values to the variables, etc. in the bean instance. The only catch is there are a pool of identical instances and you are not guaranteed to get the exact same instance on every call. For each call, you get whatever instance happens to be available. This is identical to checking out a book from the library or renting a movie from the video store. You are essentially checking out or renting a new bean instance on each method call.

With EJB 3.0, it's now possible to write stateless session bean without specifying a deployment descriptor; you basically have to write just a remote or local business interface, which is a plain-old-java-interface,

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annotated

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with

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the

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@Remote

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or

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@Local

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annotation

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the

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stateless

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session

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bean

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implementation,

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a

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plain-old-java-object

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which

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implements

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the

...

remote

...

or

...

the

...

local

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business

...

interface

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and

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is

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annotated

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with

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the

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@Stateless

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annotation

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This

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example

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is

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the

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"simple-stateless"

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example

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located

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in

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the

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openejb-examples.zip

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available

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on

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the

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download

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page.

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The Code

In this example we develop a simple EJB 3 Stateless session EJB. Every stateless session bean implementation must be annotated using the annotation @Stateless or marked that way in the ejb-jar.xml

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file.

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Our

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Stateless

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bean

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has

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2

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business

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interfaces:

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CalculatorRemote,

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a

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remote

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business

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interface,

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and

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CalculatorLocal,

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a

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local

...

business

...

interface.

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A

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minimum

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of

...

one

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business

...

interface

...

is

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required.

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Bean

...

In

...

EJB

...

3.0

...

session

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beans

...

do

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not

...

need

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to

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implement

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the

...

javax.ejb.SessionBean

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interface.

...

You

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can

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simply

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annotate

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it

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as

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@Stateless

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if

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you

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want

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it

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to

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be

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a

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stateless

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session

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bean.

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Users

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of

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EJB

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2.x

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may

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notice

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the

...

bean

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actually

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implements

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the

...

business

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interfaces!

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In

...

the

...

prior

...

version

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of

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EJB

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implementing

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the

...

remote

...

interface

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(which

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derives

...

from

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javax.ejb.EJBObject)

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in

...

your

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bean

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was

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just

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not

...

allowed.

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Now

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there

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is

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no

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javax.ejb.EJBObject

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requirement,

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so

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implementing

...

the

...

business

...

interfaces

...

is

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standard

...

practice

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for

...

EJB

...

3.0.

...

Local

...

business

...

interface

...

...
Local
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interfaces
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in
...
EJB
...
are
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pass-by-reference
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interfaces.
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Meaning
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that
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normal
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java
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semantics
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are
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used
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for
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passing
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arguments,
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return
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values
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and
...
exceptions.
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A
...
business
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local
...
interface
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can
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be
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any
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plain
...
java
...
interface.
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There
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are
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no
...
restrictions
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on
...
the
...
method
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arguments,
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return
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types,
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or
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throws
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clauses.
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Unless
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specified
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otherwise,
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every
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interface
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your
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bean
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implements
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(and
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it's
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parent
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class
...
implements
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and
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so
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on)
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is
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considered
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to
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be
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a
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local
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business
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interface.
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You
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can
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use
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the
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@Local
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annotation
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to
...
explicitly
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state
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that
...
an
...
interface
...
is
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a
...
local
...
interface,
...
but
...
this
...
is
...
not
...
required.
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You'll
...
notice
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that
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in
...
EJB
...
3.0
...
the
...
Local
...
Business
...
Interface
...
of
...
a
...
stateless
...
session
...
bean
...
does
...
not
...
need
...
to
...
extend
...
from
...
javax.ejb.EJBLocalObject
...
and
...
does
...
not
...
need
...
a
...
javax.ejb.EJBLocalHome
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interface
...
as
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they
...
did
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in
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EJB
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2.x
...
and
...
prior.
...
Per
...
the
...
vocabulary
...
of
...
the
...
EJB
...
spec,
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interfaces
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that
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implement
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javax.ejb.EJBLocalObject
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or
...
javax.ejb.EJBLocalHome
...
are
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considered
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Component
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Interfaces
...
and
...
the
...
plain
...
java
...
interface
...
above
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is
...
considered
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a
...
Business
...
Interface.
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Remote

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business

...

interface

...

...
Remote
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interfaces
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are
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pass-by-value
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interfaces.
...
Meaning
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that
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all
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method
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parameters,
...
return
...
values,
...
and
...
exceptions
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are
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serialized
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on
...
every
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call.
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The
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result
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is
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that
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you
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get
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a
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copy
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of
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the
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original
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object
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and
...
not
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the
...
original
...
object.
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The
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advantage
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is
...
of
...
course
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that
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Remote
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interfaces
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can
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be
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used
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to
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invoke
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an
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EJB
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across
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a
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network
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in
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a
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client-server
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fashion.
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There
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are
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no
...
restrictions
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on
...
the
...
Remote
...
interface
...
itself,
...
but
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there
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are
...
on
...
the
...
data
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passed
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in
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and
...
out
...
of
...
the
...
remote
...
interface.
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The
...
values
...
passed
...
into
...
a
...
method
...
or
...
returned
...
from
...
a
...
method
...
of
...
a
...
Remote
...
interface
...
must
...
be
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serializable
...
.
...
It
...
is
...
fine
...
for
...
the
...
method
...
signature
...
to
...
be,
...
for
...
example,
...
"public
...
Object
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myMethod(Object
...
myParam)"
...
as
...
long
...
as
...
the
...
value
...
passed
...
in
...
and
...
returned
...
implements
...
java.io.Serializable
...
.
...
As
...
stated
...
above,
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the
...
Remote
...
Business
...
Interface
...
of
...
a
...
bean
...
can
...
be
...
any
...
plain
...
old
...
interface.
...
It
...
does
...
not
...
need
...
to
...
extend
...
javax.ejb.EJBObject,
...
it
...
does
...
not
...
need
...
a
...
javax.ejb.EJBHome,
...
the
...
methods
...
do
...
not
...
need
...
to
...
throw
...
javax.rmi.RemoteException,
...
and
...
the
...
bean
...
class
...
can
...
implement
...
it!
...
At
...
minimum
...
the
...
interface
...
must
...
be
...
annotated
...
with
...
@Remote
...
either
...
in
...
the
...
interface
...
itself
...
or
...
in
...
the
...
bean
...
class,
...
or
...
the
...
interface
...
must
...
be
...
declared
...
via
...
<business-remote>
...
in
...
the
...
ejb-jar.xml.
...

Writing

...

a

...

unit

...

test

...

for

...

the

...

example

...

Writing
...
an
...
unit
...
test
...
for
...
the
...
stateless
...
session
...
EJb
...
is
...
quite
...
simple.
...
We
...
need
...
just
...
to
...
write
...
a
...
setup
...
method
...
to
...
create
...
and
...
initialize
...
the
...
InitialContext,
...
and
...
then
...
write
...
our
...
test
...
methods
...

setUp

...

Test

...

the

...

local

...

business

...

interface

...

Test

...

the

...

remote

...

business

...

interface

...

...
Note
...
that
...
JNDI
...
names
...
for
...
Java
...
SE
...
clients
...
are
...
not
...
standardized
...
by
...
the
...
EJB
...
spec.
...
This
...
is
...
unfortunate
...
and
...
something
...
being
...
addressed
...
in
...
EJB
...
3.1.
...
The
...
default
...
schema
...
that
...
OpenEJB
...
uses
...
is
...
ejbName
...
+
...
interfaceType
...
(i.e.
...
Local,
...
Remote,
...
LocalHome,
...
RemoteHome),
...
so
...
in
...
our
...
example
...
"CalculatorImpl"
...
+
...
"Local"
...
and
...
"CalculatorImpl"
...
+
...
"Remote".
...
You
...
can
...
in
...
fact
...
change
...
this
...
default
...
to
...
be
...
absolutely
...
anything
...
you
...
want
...
including
...
interface
...
class
...
name,
...
ejb
...
class
...
name,
...
and
...
more.
...

Running

Running the example is fairly simple. In the "simple-stateless"

...

Child pages

Versions Compared

Old Version 22

New Version Current

Key

Overview

The Code

Bean

Local

business

interface

Remote

business

interface

Writing

a

unit

test

for

the

example

setUp

Test

the

local

business

interface

...

Test

the

remote

business

interface

Running

Child pages

Page History

Versions Compared

Old Version 22

New Version Current

Key

Overview

The Code

Bean

Local

business

interface

Remote

business

interface

Writing

a

unit

test

for

the

example

setUp

Test

the

local

business

interface

...

Test

the

remote

business

interface

Running